1. Field of the Invention
The invention generally relates to systems that may be used in performing joint surgery; with a particular embodiment of the invention being described, without limitation, in the context of knee arthroplasty. More particularly, with respect to knee arthroplasty, the invention relates to systems used to properly locate and guide instruments that resect bone in order to achieve a proper cut; and facilitate the proper location and installation of artificial femoral and tibial prosthetic components.
2. Brief Description Of The Prior Art
Total knee arthroplasty involves the replacement of portions of the patellar, femur and tibia with artificial components. In particular, a proximal portion of the tibia and a distal portion of the femur are cut away (resected) and replaced with artificial components.
As used herein, when referring to bones or other body parts, the term “proximal” means closest to the heart and the term “distal” means more distant from the heart. When referring to tools and instruments, the term “proximal” means closest to the practitioner and the term “distal” means distant from the practitioner.
There are several types of knee prostheses known in the art. One type is sometimes referred to as a “resurfacing type”. In these prostheses, the articular surface of the distal femur and proximal tibia are “resurfaced” with respective metal and plastic condylar-type articular bearing components.
The femoral component is typically a metallic alloy construction (cobalt-chrome alloy or 6A14V titanium alloy) and provides medial and lateral condylar bearing surfaces of multi-radius design of similar shape and geometry as the natural distal femur or femoral-side of the knee joint.
One important aspect of these procedures is the correct resection of the distal femur and proximal tibia. These resections must provide planes which are correctly angled in order to properly accept the prosthetic components. In particular, the resection planes must be correctly located relative to three parameters: proximal-distal location, varus-valgus angle and flexion-extension angle.
U.S. Pat. No. 5,916,219 (hereby incorporated by reference) discloses an apparatus and method for tibial alignment which allows the independent establishment of two separate geometric planes to be used as a reference for the cutting of the tibial plateau during total knee arthroplasty.
Two separate frame assemblies with telescoping rods are attached to the tibia with a fixed relative angle between them, thereby allowing alignment with the mechanical axis of the bone. A cutting block is mounted on one of the assembly frames and is positioned against the tibia. Stabilizing pins are then placed in the cutting block, allowing the proper tibial plateau resection plane to be created.
The apparatus and method taught in the '219 patent, while solving many prior art problems as indicated therein, has a few disadvantages. The alignment apparatus must be removed prior to performing resection. The device ratchets to discrete locations, preventing a smooth (hereinafter defined as an “infinitely adjustable”) alignment. Further, the device can only be used to resect the tibia and cannot be used for femoral resection.
Recently, various computerized systems have been introduced to aid the practitioner during different surgical procedures. A typical, commercially available system is described in the attached Appendix. Such systems typically include multiple video cameras which are deployed above and around the surgical site; and a plurality of dynamic reference frame (DRF) devices, also known as trackers, which are attached to body parts and surgical instruments.
The trackers are generally LED devices which are visible to the cameras. Using software designed for a particular surgical procedure, a computer receiving input from the cameras guides the placement of surgical instruments.
The prior art instruments used for determining the correct planes for tibial and femoral resection in total knee arthroplasty are not well suited for use with computerized systems. The known tools utilize either intra-medullary alignment or extra-medullary alignment techniques and movement in three degrees of freedom is difficult or impossible. Moreover, in order to be useful with computer aided navigation systems, trackers must be attached to the tools. Existing tools do not permit or readily facilitate the attachment of trackers.
Although computer aided navigation systems are superior to unaided visual navigation by the practitioner, computers have known faults. As every computer user knows, any computer can crash or fail in such a way that it may take hours to repair. This is unacceptable during a surgical procedure. Therefore, it is necessary to provide a backup system of some kind so that the procedure may be completed without the failed computer.